Minimization of volatile organic sulphur byproducts in dimethyl sulfate quaternization of amines made with hypophorous acid

ABSTRACT

The present invention relates to a process for the minimization of volatile organic sulphur byproducts in dimethyl sulfate quaternization of amines made with hypophosphorous acid, which leads to the formation of an odor stable product.

The present case is based on International Application No.PCT/EP2003/014890 filed on Dec. 23, 2003, which claims priority of U.S.Provisional application No. 60/437,474 filed on Jan. 2, 2003.

FIELD OF THE INVENTION

The present invention relates to a process for the minimization ofvolatile organic sulphur byproducts in dimethyl sulfate quaternizationof amines made with hypophorous acid, which leads to the formation of anodor stable product.

BACKGROUND OF THE INVENTION

Quaternized fatty acid triethanolamine ester salts are cationicsurfactants which are excellent fabric-softeners that have highecotoxicological compatibility. Ester quats are typically produced in atwo-stage process in which triethanolamine is first partly esterifiedwith fatty acids and the reaction product is subsequently alkylated orquaternized with an alkylating agent. Hypophosphorous acid and sodiumhypophosphite are preferred catalysts for the esterification step.However, during working up, particularly at relatively hightemperatures, certain by-products are formed, resulting in an adverseeffect on the odor of the quaternized product. The present inventionprovides a process for the production of quaternized fatty acidtriethanolamine ester salts having minimal odor problems. Morespecifically, the invention provides a process for the minimization ofvolatile organic sulphur byproducts in dimethyl sulfate quaternizationof amines made with hypophorous acid, which leads to the formation of anodor stable product.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process for the minimization ofvolatile organic sulphur byproducts in dimethyl sulfate quaternizationof amines made with hypophorous acid, which leads to the formation of anodor stable product. The process of the invention is especially usefulin the production of color- and odor-stable quaternized fatty acidtriethanolamine ester salts.

Dimethyl Sulfate quaternaries are typically made in two steps. The firststep is to esterfy the starting ethanolamine, for exampletriethanolamine, with fatty acid in the presence of an esterificationcatalyst/reductive bleaching agent, i.e., for example, hypophosphorousacid. The second step is to quaternize the esteramine withdimethylsulfate in order to form the ester quaternary ammonium compound.The synthesis of ester quaternaries can, however, result in a productthat exhibits a foul objectionable odor. The present inventors havedetermined that the cause of this objectionable odor is a small amountof sulfur dioxide impurity in the dimethyl sulfate alkylating agent.More particularly, the sulfur dioxide impurity in the dimethyl sulfateis, under quaternization conditions, partially converted to hydrogensulfide, methyl mercaptan, dimethyl sulfide and dimethyl disulfide, andother odor causing by-products in trace form. These undesirableby-products are the source of objectionable odors in the final product.Accordingly, the present invention is based on the discovery that sulfurdioxide is the source of odor by-products in the production of dimethylsulfate quaternaries. By extension, if the sulfur dioxide is removed orminimized in the dimethyl sulfate, then the sulfur by-productconcentrations will be minimized and improve the odor profile of thefinal product.

The present inventors have discovered a process for the production ofodor stable products prepared from the dimethyl sulfate quaternizationof amines made with hypophosphorous acid. Such products are odor stablebecause the volatile organic sulphur by-products which lead to theformation of objectionable odors are minimized. In this regard theinvention comprises quaternizing said amines with a dimethyl sulfatequaternization agent wherein said dimethyl sulfate has a sulfur dioxidecontent of less than 10 parts per million (ppm), preferably less than 8ppm, and still more preferably less than 5 ppm. Minimizing the sulfurdioxide content in the dimethyl sulfate quaternization agent reduces oreliminates the formation of undesirable odor causing by-products such ashydrogen sulfide, methyl mercaptan, dimethyl sulfide and dimethyldisulfide, resulting in a greatly improved odor profile of the finalproduct. The present invention is not limited to processes for thepreparation of ester quats but rather, is applicable to any dimethylsulfate quaternization process of amines made with esterificationcatalyst/reductive bleaching agents.

The esterification catalyst/reductive bleaching agents employed in thecontext of the present invention are characterized in that theytypically have a standard reduction potential of at least 0.5 volts.Nonlimiting examples of such esterification catalyst/reductive bleachingagents are hypophosphorous acid, sodium hypophosphite and mixturesthereof.

In another embodiment, the present invention relates to quaternaryammonium compounds having particularly good performance and stabilityprofiles obtained by reaction of C₁₂-C₂₂ fatty acids or thehydrogenation products thereof, or a mixture of such acids, with analkanolamine in the presence of an acid catalyst, wherein the ratio offatty acid to alkanolamine is from about 1.40-2.0. The resultantesteramine reaction products are subsequently quaternized to obtain thequaternary ammonium salts of the present invention.

The fatty acid is preferably a C₁₆-C₂₂ acid containing a degree ofunsaturation such that the iodine value (“IV”) is in the range of fromabout 0-140, preferably, from about 3-90, more preferably in the rangeof 40-60 and still more preferably, in a range of from about 45-55.Preferably, the fatty acid source is selected from C₁₂-C₂₂ fatty acidsrepresented by the formula:R_(x)—COOH,wherein, R_(x) is a C₁₁-C₂₁ alkyl group.

Preferred sources of C₁₂-C₂₂ fatty acids are selected from the groupconsisting of: lauric acid, tridecylic acid, myristic acid, pentadecylicacid, palmitic acid, margaric acid, stearic acid, arachidic acid,phytanic acid, behenic acid, anionic derivatives thereof, salts thereof,and combinations thereof.

Preferred sources of acid are C₁₂-C₂₂ fatty acids comprising a saturatedalkyl group. Other preferred sources of acids are C₁₂-C₂₂ fatty acidscomprising an unsaturated group, typically having an iodine value offrom 15 to 25, preferably from 18 to 22.

The source of acid may be selected from the group consisting ofpalmitoleic acid, oleic acid, elaidic acid, vaccenic acid, linoleicacid, cis-eleostearic acid, trans-eleostearic acid, linolenic acid,arachidonic acid, anionic derivatives thereof, salts thereof, andcombinations thereof.

Preferred sources of fatty acids are selected from the group consistingof coconut, soybean, tallow, palm, palm kernel, rapeseed, lard,sunflower, corn, safflower, canola, olive, peanut, and combinationsthereof. A preferred source of acid is hard tallow fatty acid and/orpartially hydrogenated tallow fatty acid.

Preferred fatty acids include but are not limited to oleic, palmitic,erucic, eicosanic and mixtures thereof. Soy, tallow, palm, palm kernel,rape seed, lard, mixtures thereof and the like are typical sources forfatty acid which can be employed in the present invention. The fattyacid(s) employed in the present process optionally have a cis to transisomer ratio of from about 80:20 to about 95:5. In another embodiment,the trans isomer content of said fatty acid(s) is less than about 10%.An typical trans-isomer content is between about 0.5-9.9%. A preferredfatty acid is a mixture of tallow/distilled tallow having a cis:transisomer ratio of greater than 9:1. Partial or fully hydrogenated fattyacids can be employed in the process of the present invention.

The alkanolamines employable in the present invention generallycorrespond to the formula:

herein R, R₁ and R₂ are independently selected from C₂-C₆ hydroxyalkylgroups or a group of the formula

where R₃ is independently H or a C₁ to C₄ alkyl and z is 1 to 10.

Alternatively, the alkanolamines can be of the formula:

Where R₄ is a linear or branched, substituted or unsubstituted alkylgroup, amidoalkyl group, etheralkyl group, or polyoxyalkylene group, nand m=1-10, and R₃ has the meanings defined above.

Examples of alkanolamines useful in the context of the present inventioninclude, but are not limited to, triethanolamine, propanoldiethanolamine, ethanol diisopropanolamine, triisopropanol amine,diethanolisopropanol amine, diethanolisobutanolamine, methyldiethanolamine and mixtures thereof.

The molar ratio of fatty acid to alkanol amine is generally in the rangeof from about 1.4 to 2.0, preferably from about 1.55-1.90, and morepreferably, in the range of from about 1.65-1.75. Best results areusually obtained when the molar ratio is between about 1.68-1.72. Theacid catalyst employable in the present process includes, but is notlimited to, acid catalysts such as sulfuric acid, phosphorous acid,p-toluene sulphonic acid, methane sulphonic acid, oxalic acid,hypophosphorous acid or an acceptable Lewis acid in an amount of500-3000 ppm based on the amount of fatty acid charge. A preferred acidcatalyst is hypophosphorous acid. Typically, 0.02-0.2% by weight, andmore preferably 0.1 to 0.15% by weight of acid catalyst, based on theweight of fatty acid, in employed in the present process.

The esterification of fatty acids with alkanolamines is carried out at atemperature of from about 150°-250° C. until the reaction product has anacid value of below 5. After the esterification, the crude product isreacted with alkylating agents in order to obtain the quaternaryammonium product. The alkylating agent employed in the present inventionis dimethyl sulfate having a sulfur dioxide content of less than about20 ppm, in another embodiment less than 10 ppm, in another embodimentless than 8 ppm, and in yet another embodiment less than 5 ppm.Typically, 0.7 to 1.0, preferably 0.75 to 0.98 mol dimethyl sulfate permole of esteramine is satisfactory in yielding the quaternized product.

The quaternization may be carried out in bulk or in solvent, attemperatures ranging from 60°-120° C. If a solvent is employed, then thestarting materials and/or product must be soluble in the solvent to theextent necessary for the reaction. Solvents of this type are generallyknown in the art. Suitable examples include polar solvents such as, forexample, lower alcohols, i.e., C₁-C₆ alcohols. Other solvents which canbe employed include, but are not limited to mono-, di-, andtri-glycerides, fatty acids, glycols and mixtures thereof.

The products of the invention can beneficially be employed in textilesoftening and/or personal care compositions and in other applicationstypical for cationic surfactants.

The invention will now be illustrated by the following non-limitingexamples.

EXAMPLE 1 Quaternization of TEEMA (Tallow Fatty Acid Esters ofTriethanolamine)

In a 500 ml 3-necked flask we placed 250.3 g (0.386 mol) of HT (hardenedtallow) TEEMA (Pilot Plant batch 2279) containing 320 ppm of residualhypophosphorous acid. We treated this at 75-90° with a total of 45.6 g(0.361 mol) of dimethyl sulfate containing 7 ppm of sulfur dioxide by GCanalysis. After the addition, the reaction was held at 90° for 1 hrbefore 30 g of isopropyl alcohol was added to make the final TEQ (methylquaternary ammonium salt of triethanolamine esters).

COMPARATIVE EXAMPLE 1

We used the same procedure and ingredients of Example 1 except thatstandard commercial dimethyl sulfate containing 984 ppm of sulfurdioxide was employed.

The TEQ from the above examples was formulated into fabric softenercompositions whose odors were compared by a panel. In addition, bothquat samples were analyzed for sulfur-containing species by GC. Resultsare summarized in the table below.

TEQ Made from Low- and High-SO2 DMS Analysis Example 1 Comp. Ex. 1 SO2in DMS 7 ppm 984 ppm Malodor detected? No Yes CH3SH by GC Not detected(<2 ppb)  6 ppb

1. A process for the minimization of odor in dimethyl sulfatequaternization of amines made with hypophorous acid which comprisesconducting said quaternization in the presence of dimethyl sulfate,wherein said dimethyl sulfate contains less than 20 ppm sulfur dioxide.2. The process of claim 1 wherein said odor is caused by volatileorganic sulphur byproducts.
 3. The process of claim 2 wherein saiddimethyl sulfate contains less than 8 ppm sulfur dioxide.
 4. The processof claim 3 wherein said dimethyl sulfate contains less than 5 ppm sulfurdioxide.
 5. A process for preparing an ester quaternary having improvedodor profile with comprises esterfying an alkanol amine with fatty acidin the presence of a esterification catalyst/reductive bleaching agenthaving a standard reduction potential of at least 0.5 volts in order toform an esteramine and thereafter quaternizing said esteramine withdimethylsulfate, wherein said dimethyl sulfate contains less than 20 ppmsulfur dioxide.
 6. The process of claim 5 wherein said esterificationcatalyst/reductive bleaching agent is selected from the group consistingof hypophosphorous acid, sodium hypophosphite and mixtures thereof. 7.The process of claim 6 wherein said fatty acid is a C₁₆-C₂₂ acidcontaining a degree of unsaturation such that the iodine value (“IV”) isin the range of from about 0-140.
 8. The process of claim 7 wherein saidfatty acid is selected from the group consisting of oleic, palmitic,erucic, eicosanic and mixtures thereof.
 9. The process of claim 8wherein said alkanol amine is of the formula:

wherein R, R₁ and R₂ are independently selected from C₂-C₆ hydroxyalkylgroups.
 10. The process of claim 9 wherein said alkanolamine is selectedfrom the group consisting of triethanolamine, propanol diethanolamine,ethanol diisopropanolamine, triisopropanol amine, diethanolisopropanolamine, diethanolisobutanolamine, methyl diethanolamine and mixturesthereof.
 11. The process of claim 5 wherein said dimethyl sulfatecontains less than 8 ppm sulfur dioxide.
 12. The process of claim 11wherein said dimethyl sulfate contains less than 5 ppm sulfur dioxide.